The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.
A quantum computer can greatly increase the processing speed compared to the conventional computing method, by using a quantum algorithm that is totally different from that for a conventional computer. Advances in the quantum computing technology caused the conventional Rivest Shamir Adleman (RSA)-based encryption system to be easily deciphered, and hence a quantum key distribution (QKD) system has been developed to replace the conventional encryption system, which has been already commercialized by several companies and in practical use.
The principal limitation of the current QKD system is that there exists a limit on the distance for a single time communication due to an attenuation of a single photon while propagating through an optical fiber. In order to overcome the shortcoming, signals need to be amplified by using a quantum repeater. An ion trap is most popular among the methods for realizing a quantum memory that is indispensable for manufacturing the quantum repeater.
Ion traps have a basic structure formed by four electrodes e1, e2, e3 and e4, as shown in FIG. 1A. When the electrodes e1 and e4 are grounded and a high voltage radio frequency (RF) signal is applied to the electrodes e2 and e3 to form an electric field (E) as shown in FIG. 1B, electrically charged particles are forced, on average, towards the center of the quadrangle (e.g., a square) defined by the electrodes e1, e2, e3 and e4. The potential generated by such average force is referred to as a ponderomotive potential.
FIG. 1C is a diagram showing the shape of a ponderomotive potential Φpp formed by the electrodes e1, e2, e3 and e4, wherein the ponderomotive potential is irrelevant to the sign of a charged particle trapped by the electrodes e1, e2, e3 and e4. The potential continues to centrally attract the charged particle despite its tendency to depart from the z-axis (FIG. 1A), but the potential does not contribute to determining the location where the charged particle may be trapped along the z-axis. Therefore, in order to trap the electrically charged particle at the location as in FIG. 1A, a voltage is applied to satisfy the condition of V1>V2, instead of grounding the electrodes e1 and e4.
The ion trap can be manufactured by various methods. Among them the most popular one is a MEMS-based 3D ion trap manufacturing. Since the introduction of the concept of applying the ion trap to the quantum computer, MEMS-based planar ion trap chips or surface ion trap chips are manufactured by forming metal electrodes on a silicon substrate as shown in FIG. 2A, featuring ions trapped at a position as high as several tens to hundreds of micrometers above the ion trap device as shown in FIG. 2B. In contrast to this, a MEMS-based 3D ion trapping technology can generally increase the life of the ion by securing more potential depth than with the planar ion trap chip.
As shown in FIG. 3, the MEMS-based ion trap chip traps an ion by using an electric field formed by a high-voltage RF signal and a direct-current (DC) voltage in an ultra-high vacuum (UHV) environment. At this moment, a high voltage of up to several hundred volts is applied to an RF electrode. As opposed to a low-voltage RF signal which might be safely applied to the RF electrode, the high-voltage RF signal applied to the RF electrode has a high tendency to cause a breakdown to take place between the RF electrode and peripheral electrodes. For example, when a breakdown occurs between the RF electrode and a DC electrode, they are both damaged, disabling the ion trap chip.
A way to cope with this issue includes broadening a space between the RF electrode and the DC electrode to prevent a potential breakdown; however, this causes a degradation of the performance of the ion trap chip. Therefore, in order to increase the life of the trapped ion, a laser is used to decrease the kinetic energy of the ion to cool down the ion.
As an example of the limited ion trap chip for solving the breakdown issue so as to avoid affecting the performance of a conventional MEMS-based 3D ion trap chip, an ion trap chip is known to be dimensioned as illustrated in FIG. 3A wherein the number of electrodes is increased to control an ion in a precise and various manner or an interval between the electrodes is minimized to downsize the ion trap chip having electrodes formed by Au plating on both surfaces of the silicon substrate, so that the ion is trapped at the center portion of the silicon structure.
Therefore, an approachable range of the laser is limited to an area of passing a slot for injecting or loading the ion(s) as shown in FIG. 3B, and hence as the ion injecting slot in the ion trap device gets smaller, a laser scattering is likely to happen. For this reason, there is a limit in decreasing the size of the ion trap device. To cope with this problem, a separate path for the laser is needed to minimize the breakdown. To this end, a new process is required for providing a hole that allows a laser emitted in a first direction of the ion trap device to penetrate through the ion trap device to pass in a second direction in the ion trap device without damaging the ion trap chip or for manufacturing the ion trap chip with the hole formed therein.